The present invention relates generally to rangefinder systems and more particularly to passive optical rangefinder systems.
Frequently, both in commercial and in military situations, it is necessary to determine both the identity and location of an unknown object. The most common method to determine an object's location has been to use radar. The advantage of radar systems is that various other parameters of the object can be determined with great accuracy, such as, its speed and direction. The primary disadvantage, however, with such systems is that they have poor resolution rendering identification of the unknown object virtually impossible. Therefore, objects which can be located very closely with regard to position and speed normally cannot be otherwise identified since they appear to the radar viewer as no more than a blip or several blips on the face of a cathode ray tube. However, some advances have been made in radar technology. Complex and expensive monopulse radar systems have been developed which depend on extremely high frequency signals and intricate processing equipment to reconstruct radar images of the object to be identified.
Active optical rangefinding systems on the other hand make it quite easy to identify unknown objects but require great skill to obtain correct range information. In addition, expensive mechanical devices are needed to move the optics with precision sufficient to determine range.
Other active optical rangefinder systems have been developed which make use of gated laser beams, such as gated gallium arsenide lasers, in combination with a gated low level light television camera to provide simultaneous range and optical image information. However, these systems require liquid nitrogen cooling to 77.degree. K with refills of liquid nitrogen about every 10 hours which is expensive and inconvenient to operate. In addition, these systems are somewhat less effective during the day when bright background skies limit the sensitivity and therefore the range of the system.